Nitrogenous compounds as indicators of nitrogen saturation in Scots pine, Norway spruce and other boreal forest plants

This study investigated the relationships between rates of nitrogen deposition, nutrient imbalances, and the content of arginine, other amino acids and putrescine in a variety of boreal forest plants. The feasibility of using these compounds as indicators of nitrogen saturation or potassium deficiency in Norway spruce (Picea abies (L.) Karst), Scots pine (Pinus sylvestris) and other boreal species was evaluated. Firstly, the effect of nitrogen deposition and site quality on amino acid concentrations in needles of Norway spruce and Scots pine were studied in two areas with different levels of nitrogen deposition. Secondly, the relationships between nitrogen deposition and accumulation of amino acids in boreal field layer species was analysed. Thirdly, the effect of improved nutrient balance on arginine concentrations in heavily nitrogen-fertilized Scots pine trees was investigated. Finally, the usefulness of arginine and putrescine as indicators of potassium deficiency was investigated in a potassium deficient Norway spruce stand. Concentrations of arginine in the needles of both spruce and pine increased with decreasing site index, and the highest concentrations of arginine were found in the area, with the highest deposition of nitrogen. The data also showed that field layer species exposed to high levels of nitrogen will accumulate nitrogen in specific amino acids. The results suggested that arginine may be used as an indicator on nitrogen excess in conifers, and that the concentrations of specific amino acids in different field layer species may be used as indicators of nitrogen excess in the ecosystem. Improved mineral nutrient balance was reflected in decreased arginine levels in needles of Scots pine. In addition, it was demonstrated that when nitrogen supply is reduced the arginine concentration also decreases as an effect of reduced nitrogen supply per se. Furthermore, it was found that both arginine and putrescine may be used as indicators of potassium deficiency in Norway spruce, although putrescine may be a more sensitive indicator.